1. Field of the Invention
The present invention relates to a method for piecing a fasciated yarn. More specifically, it relates to a method for piecing a yarn end to a fiber bundle in a fasciated yarn spinning unit when the yarn breaks during the spinning operation.
2. Description of the Prior Art
In a fasciated yarn spinning unit, a fiber bundle of a ribbon-like shape (hereinafter referred to as a fleece) delivered from a front roller pair of a drafting means is sucked into an air nozzle disposed just downstream of the front roller pair. The fleece is false-twisted in the air nozzle by a vortex generated therein and is converted to a so-called fasciated yarn. This spinning system is very advantageous because it can run at a much higher rate of 100 m/min, compared to a conventional spinning system such as ring spinning or open-end spinning.
A problem has arisen in this spinning system in that the yarn is difficult to be pieced when it has broken during the spinning operation because of the compact structure of the yarn, due to the entanglement of a surface fiber around a core portion of the yarn, as well as the high processing speed it is almost impossible to piece the broken end of the yarn to a freshly delivered fleece by merely superposing them together in the twisting zone. Thus, it is necessary to reversely guide the broken end through the air nozzle into the drafting means so as to superpose it on the fleece in a drafting zone. This is referred to as "threading" hereinafter.
A method for the abovesaid threading operation has been disclosed in, for example, Japanese Unexamined Patent Publication (Kokai) No. 53-35033. According to the prior art method, the air nozzle has inclined jets in an inner wall thereof for reversely transporting the yarn from an outlet to an inlet of the air nozzle by an air stream ejected from the jets. The broken end of the yarn is sucked into the air nozzle from the outlet thereof by the above-mentioned air stream and is exited from the inlet of the air nozzle. Then, it is nipped by a front roller pair of a drafting means. A problem of this prior art method is that the suction force caused by the air stream ejected from the jets is so small that the yarn end disposed in front of the outlet of the air nozzle is difficult to be introduced thereinto or, even if sucked in, it is often prevented from smooth threading due to fluffs.
One solution of the above-mentioned problem is the provision of a suction tube connected to a powerful suction source. A mouth thereof is applied to the inlet of the air nozzle when the yarn piecing operation is carried out to suck the yarn end from the outlet of the air nozzle. However, since the air nozzle in the conventional unit is disposed close to the front roller pair, in order to well receive the fluffy fleece delivered from the latter, there is only a small space therebetween. Accordingly, the mouth of the suction tube has to be small-sized to fit the small space. This causes lack of suction force and, in turn, unsatisfactory threading operation.